1. Field of the Invention
This invention relates to a device for developing an electrostatic latent image formed on an image bearing member and in particular to a developing device using a single component or magnetic developer suitable for use in image processing machines, such as electrophotographic copiers, facsimile machines and printers.
2. Description of the Prior Art
FIG. 1 schematically illustrates a prior art developing device of the type in which a single component or magnetic developer is transported cyclically along a predetermined path thereby applying the developer to an image bearing member on which an image to be developed is carried. The developing device of FIG. 1 includes a developing sleeve 2 which is supported to be driven to rotate in the direction indicated by the arrow. Onto the peripheral surface of the sleeve 2 is supplied toner 1 from a hopper 3, and as the sleeve 2 rotates, the toner 1 supplied to the sleeve 2 is regulated in thickness by means of a doctor blade 4, which is disposed at the downstream side of the hopper 3, so that there is formed a thin layer of electrically charged toner on the sleeve 2. Then, as the sleeve 2 further rotates, the toner layer thus formed is brought to a developing station D where the sleeve 2 is in rolling contact with an imaging belt 5 on which an electrostatic latent image is carried. At the developing station, the toner is selectively transferred from the sleeve 2 to the belt 5 in accordance with the charge pattern defined by the latent image so that the latent image is developed into a visible image. Thus, the toner layer on the sleeve 2 after the developing station D is irregular in thickness.
The developing device of FIG. 1 also includes a scraper 6 as fixedly mounted on a wall defining part of the hopper 3 with its free end in sliding contact with the developing sleeve 2. Thus, the toner remaining on the sleeve 2 is once removed from the sleeve by the scraper 6 and the thus removed toner is transported into the hopper 3 as passing through holes 6a provided in the scraper 6 so that it comes to be mixed with the toner stored in the hopper 3. Then, with the rotation of the developing sleeve 2, the recovered toner is well mixed with the toner stored in the hopper 3 at a stagnation area S, whereby the toner of uniform quality is prepared to be supplied to the developing sleeve 2 for the subsequent developing cycles.
The scraper 6 is typically comprised of an elastic material and it is typically provided with its base end fixedly mounted, for example, on a housing of hopper 3 and its free end pressed against the developing sleeve 2 disposed in a counter direction with respect to the direction of transportion of the toner carried on the sleeve 2 at the point of contact between the sleeve 2 and the scraper 6. With such a scraper 6, when fluctuation occurs in the thickness of the toner film on the sleeve 2 and/or the level of frictional force at the contact between the sleeve 2 and the scraper 6, unstability is created in the scraping function. Difficulty also exists in manufacturing and mounting the scraper 6 accurately. Therefore, there has been a need to provide a developing device having an improved scraping performance.